This commit adds a new `_ml/trained_models/{model_id}/_infer` API. This api works for both native NLP models and supervised models trained via Data Frame analytics.
The format of the API is the same as the old `_ml/trained_models/{model_id}/deployment/_infer`. Taking a `docs` and an `inference_config` parameter.
This PR also deprecates the old experimental `_ml/trained_models/{model_id}/deployment/_infer` API.
The biggest difference is that the response now nests all results under an "inference_results" object.
closes: https://github.com/elastic/elasticsearch/issues/86032
